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Omega-3 fatty acid

2007 Schools Wikipedia Selection. Related subjects: Health and medicine

      Types of Fats in Food
     * Unsaturated fat
          + Monounsaturated fat
          + Polyunsaturated fat
          + Trans fat
          + Omega: 3, 6, 9
     * Saturated fat

            See Also
     * Fatty acid
     * Essential fatty acid

   Omega-3 fatty acids are polyunsaturated fatty acids which have a C=C
   double bond in the ω-3 position. (See Nomenclature for terms and
   discussion of ω (omega) nomenclature.)

   Important omega-3 fatty acids in human nutrition are: α-linolenic acid
   (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). For
   a more complete list see List of omega-3 fatty acids. The human body
   cannot synthesize omega-3 fatty acids from scratch, but can synthesize
   all the other necessary omega-3 fatty acids from the omega-3 fatty acid
   Alpha-linolenic acid. Therefore Alpha-linolenic acid is an Essential
   nutrient which must be obtained from food, and the other omega-3 fatty
   acids which can be either synthesized from it within the body or
   obtained from food are sometimes also referred to as essential
   nutrients.

Chemistry

   Chemical structure of alpha-linolenic acid (ALA), an essential omega-3
   fatty acid, (18:3Δ9c,12c,15c). Although chemists count from the
   carbonyl carbon (blue numbering), physiologists count from the omega
   (ω) carbon (red numbering). Note that from the omega end (diagram
   right), the first double bond appears as the third carbon-carbon bond
   (line segment), hence the name "omega-3"
   Enlarge
   Chemical structure of alpha-linolenic acid (ALA), an essential omega-3
   fatty acid, (18:3Δ9c,12c,15c). Although chemists count from the
   carbonyl carbon (blue numbering), physiologists count from the omega
   (ω) carbon (red numbering). Note that from the omega end (diagram
   right), the first double bond appears as the third carbon-carbon bond
   (line segment), hence the name "omega-3"

   The term omega-3 (aka "n-3", "ω-3") signifies that the first double
   bond exists as the third carbon-carbon bond from the terminal methyl
   end (ω) of the carbon chain.

   Omega-3 fatty acids which are important in human nutrition are:
   alpha-linolenic acid (18:3, ALA), eicosapentaenoic acid (20:5, EPA),
   and docosahexaenoic acid (22:6, DHA). These three polyunsaturates have
   either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon
   atoms, respectively. All double bonds are in the cis-configuration,
   i.e. the two hydrogen atoms are on the same side of the double bond.

Biological significance

          The biological effects of the ω-3 fatty acids are largely
          mediated by their interactions with the ω-6 fatty acids, see
          Essential fatty acid interactions for detail.

   A 1992 paper by biochemist William E.M. Lands provides an overview of
   the research into omega-3 fatty acids, and is the basis of this
   section.

   The 'essential' fatty acids were given their name when researchers
   found that they were essential to normal growth in young children and
   animals. (Note that the modern definition of ' essential' is more
   strict.) A small amount of omega-3 in the diet (~1% of total calories)
   enabled normal growth, and increasing the amount had little to no
   additional benefit.

   Likewise, researchers found that omega-6 fatty acids (such as
   γ(gamma)-linolenic acid and arachidonic acid) play a similar role in
   normal growth. However they also found that omega-6 is "better" at
   supporting dermal integrity, renal function, and parturition. This led
   researchers to concentrate study on omega-6, and it is only in recent
   decades that omega-3 has become of interest.

   In 1963 it was discovered that the omega-6 arachidonic acid is
   converted by the body into pro-inflammatory agents called
   prostaglandins,. By 1979 more of what are now known as eicosanoids were
   discovered: thromboxanes, prostacyclins and the leukotrienes. The
   eicosanoids, which have important biological functions, typically have
   a short active lifetime in the body, starting with synthesis from fatty
   acids and ending with metabolism by enzymes. However if the rate of
   synthesis exceeds the rate of metabolism, the excess eicosanoids may
   have deleterious effects. Researchers found that omega-3 is also
   converted into eicosanoids, but at a much slower rate. Eicosanoids made
   from omega-3 fats often have opposing functions to those made from
   omega-6 fats (ie, anti-inflammatory rather than inflammatory). If both
   omega-3 and omega-6 are present, they will "compete" to be transformed,
   so the ratio of omega-3:omega-6 directly affects the type of
   eicosanoids that are produced.

   This competition was recognized as important when it was found that
   thromboxane is a factor in the clumping of platelets, which leads to
   thrombosis. The leukotrienes were similarly found to be important in
   immune/inflammatory-system response, and therefore relevant to
   arthritis, lupus, and asthma. These discoveries led to greater interest
   in finding ways to control the synthesis of omega-6 eicosanoids. The
   simplest way is by consuming more omega-3 and less omega-6 fatty acids.

Cardiovascular health benefits

   On September 8, 2004, the U.S. Food and Drug Administration gave
   "qualified health claim" status to eicosapentaenoic acid (EPA) and
   docosahexaenoic acid (DHA) omega-3 fatty acids, stating that
   "supportive but not conclusive research shows that consumption of EPA
   and DHA omega-3 fatty acids may reduce the risk of coronary heart
   disease."

   A 2006 report in the Journal of the American Medical Association
   concluded that their review of literature covering cohorts from many
   countries with a wide variety of demographic characteristics failed to
   demonstrate a link between omega-3 fatty acids and cancer prevention.
   This is similar to the findings of a review by the British Medical
   Journal of studies up to February 2002 that failed to find clear
   effects of long and shorter chain omega-3 fats on total mortality,
   combined cardiovascular events and cancer.

   In April 2006, a team led by Lee Hooper at the University of East
   Anglia in Norwich, UK, published a review of almost 100 separate
   studies into omega-3 fatty acids, found in abundance in oily fish. It
   concluded that they do not have a significant protective effect against
   cardiovascular disease.

   The above stands in stark contrast with two different reviews also
   performed in 2006 by the American Journal of Clinical Nutrition and a
   second JAMA review that both indicated decreases in total mortality and
   cardiovascular incidents (i.e. myocardial infarctions) associated with
   the regular consumption of fish and fish oil supplements. Of particular
   importance is that no or very few complications were documented.

   Research in 2005-06 has suggested that the in-vitro anti-inflammatory
   activity of omega-3 acids translates into clinical benefits. Cohorts of
   neck pain patients and of rheumatoid arthritis sufferers have
   demonstrated benefits comparable to those receiving standard NSAIDs.

   Those who follow a Mediterranean-style diet tend to have higher HDL
   ("good") cholesterol levels. Similar to those who follow a
   Mediterranean diet, Arctic-dwelling Inuit - who consume high amounts of
   omega-3 fatty acids from fatty fish - also tend to have increased HDL
   cholesterol and decreased triglycerides (fatty material that circulates
   in the blood). In addition, fish oil supplements containing EPA and DHA
   have been shown to reduce LDL ("bad") cholesterol and triglycerides.
   Finally, walnuts (which are rich in ALA) have been shown to lower total
   cholesterol and triglycerides in people with high cholesterol.

Omega-3 fatty acids and Autism

   According to an internet survey approximately 30% of parents use
   omega-3 supplements as a therapy for autistic children. There are
   currently only a few studies on the effectiveness of essential fatty
   acid supplementation as a treatment of autism and none of these have
   been well-controlled. Bell and colleagues reported that parents of 18
   autistic children who had been supplemented with fish oil for six
   months described improvements in overall health, cognition, sleep
   patterns, social interaction, and eye contact. Another case report
   found that an autistic child given 540 mg of EPA per day over a four
   week period experienced a complete elimination of his previous anxiety
   about everyday events as reported by his parents and clinician.

Health risks

   In a letter dated October 31, 2000 entitled Letter Regarding Dietary
   Supplement Health Claim for omega-3 Fatty Acids and Coronary Heart
   Disease, the U. S. Food and Drug Administration Centre for Food Safety
   and Applied Nutrition, Office of Nutritional Products, Labeling, and
   Dietary Supplements noted that the known or suspected risks of omega-3
   fatty acids may include:
     * Increased bleeding can occur if overused (normally over 3 grams per
       day)
     * The possibility of hemorrhagic stroke
     * Oxidation of omega-3 fatty acids forming biologically active
       oxidation products
     * Increased levels of low density lipoproteins (LDL) cholesterol or
       apoproteins associated with LDL cholesterol among diabetics and
       hyperlipidemics
     * Reduced glycemic control among diabetics
     * Suppression of immune and inflammation responses, and consequently,
       to decreased resistance to infections and increased susceptibility
       to opportunistic bacteria

   The following risks have been attributed to the FDA but are not
   mentioned in the above letter:
     * A significant potential risk is the possibility of vitamin
       poisoning from taking large doses of supplements which contain
       large quantities of vitamins (particularly vitamin A) in addition
       to omega-3 fatty acids. For this reason, the primary source of
       omega-3, if taken as a supplement, should be from fish body oil and
       not from a fish liver based oil.

Warning for persons with CHF

   Persons with congestive heart failure, chronic recurrent angina or
   evidence that their heart is receiving insufficient blood flow are
   advised to talk to their doctor before taking omega-3 fatty acids. It
   may be prudent for such persons to avoid taking omega-3 fatty acids or
   eating foods that contain them.

   In a congestive heart failure, cells that are only barely receiving
   enough blood flow become hyperexcitable. This, in turn, can lead to an
   increased risk of irregular heartbeats, which, in turn, can cause
   sudden cardiac death. Omega-3 fatty acids stabilize the rhythm of the
   heart by effectively removing these hyper-excitable cells from
   functioning, thereby reducing the likelihood of irregular heartbeats
   and sudden cardiac death. For most people, this is a very good thing
   and accounts for most of the large reduction in the likelihood of
   sudden cardiac death. However, for persons with congestive heart
   failure, the heart is barely pumping blood well enough to keep them
   alive. Omega-3 fatty acids may eliminate enough of these pumping cells
   that the heart is no longer able to pump sufficient blood to live,
   causing an increased risk of cardiac death.

Research frontiers

Psychological disorders

   Omega-3s are definitively known to have membrane-enhancing capabilities
   in brain cells. One medical explanation is that omega-3s play a role in
   the fortification of the myelin sheaths. Not coincidentally, omega-3
   fatty acids comprise approximately eight percent of the average human
   brain according to the late Dr. David Horrobin, a pioneer in fatty acid
   research. Ralph Holman of the University of Minnesota, another major
   researcher in studying essential fatty acids, who gave it the name,
   surmised how omega-3 components are analogous to the human brain by
   stating that "DHA is structure, EPA is function."

   A benefit of Omega-3s is helping the brain to repair damage by
   promoting neuronal growth. In a six-month study involving people with
   schizophrenia and Huntington's disease who were treated with EPA or a
   placebo, the placebo group had clearly lost cerebral tissue, while the
   patients given the supplements had a significant increase of grey and
   white matter.

   Consequently, the past decade of omega-3 fatty acid research has
   procured some Western interest in omega-3s as being a legitimate 'brain
   food.' Still, recent claims that one's intelligence quotient,
   psychological tests measuring certain cognitive skills, including
   numerical and verbal reasoning skills, are increased on account of
   omega-3s consumed by pregnant mothers remain unreliable and
   controversial. An even more significant focus of research, however,
   lies in the role of omega-3s as a non-prescription treatment for
   certain psychiatric and mental diagnoses and has become a topic of much
   research and speculation.

   In 1999, Andrew L. Stoll, MD and his colleagues at Harvard University
   conducted a small double-blind placebo-controlled study in thirty
   patients diagnosed with Bipolar disorder. Over the course of nine
   months, he gave 15 subjects capsules containing olive oil, and another
   15 subjects capsules containing nine grams of pharmaceutical-quality
   EPA and DHA. In doing, so he was able to make the general distinction
   between the placebo group failing to improve while the Omega-3 group
   experienced a noticeable degree of recovery. Though Stoll believes that
   the 1999 experiment was not as optimal as it could have been and has
   accordingly pursued further research, the foundation has been laid for
   more researchers to explore the theoretical association between
   absorbed omega-3s and signal transduction inhibition in the brain.
   Andrew Stoll MD also owns a company called Omegabrite that sells an
   Omega 3 oil supplement.

   Should enough research that is currently underway come to confirm the
   legitimacy of this association, then a debate and reassessment will of
   course be necessitated between Omega-3s and such prescription bipolar
   treatments as lithium, or brand Eskalith and various FDA approved and
   "off label" use pharmacologic agents. Some physicians and psychiatric
   specialists in the United States do allow willing bipolar patients to
   use Omega-3 supplements as complementary or conditional treatments.
   Omega-3s, unlike many psychopharmacologic [medication] treatments, are
   less expensive and do not commonly induce such side effects as
   diarrhea, drowsiness, and fatigue. At present, more research is needed
   before recommending that people with bipolar disorder or other mental
   illnesses take Omega-3 supplements.

The omega-6 to omega-3 ratio

   Clinical studies indicate that the ingested ratio of omega-6 to omega-3
   (especially Linoleic vs Alpha Linolenic) fatty acids are important to
   maintaining cardiovascular health.

   Both omega-3 and omega-6 fatty acids are essential, i.e. humans must
   consume them in the diet. Omega-3 and omega-6 compete for the same
   metabolic enzymes, thus the omega-6:omega-3 ratio will significantly
   influence the ratio of the ensuing eicosanoids (hormones), (e.g.
   prostaglandins, leukotrienes, thromboxanes etc.), and will alter the
   body's metabolic function. Metabolites of omega-6 are significantly
   more inflammatory (esp. arachidonic acid) than those of omega-3. This
   necessitates that omega-3 and omega-6 be consumed in a balanced
   proportion; the ideal ratio of omega-6:omega-3 being from 3:1 to 5:1.
   Studies suggest that the evolutionary human diet, rich in seafood, nuts
   and other sources of omega-3, may have provided such a ratio.

   Simopoulos, et al recommend daily intakes of three omega-3 forms: 650
   mg of EPA and DHA, and 2.22 g of ALA, and one omega-6 form: 4.44 g of
   LA. This translates to a 3:2 omega-6 to omega-3 ratio. (i.e. 1.5:1)

   Typical Western diets provide ratios of between 10:1 and 30:1 - i.e.,
   dramatically skewed toward omega-6. Here are the ratios of omega-3 to
   omega-6 fatty acids in some common oils: sunflower (no omega-3),
   cottonseed (almost no omega-3), canola 2:1, peanut (no omega-3),
   grapeseed oil (almost no omega-3) and corn oil 46 to 1 ratio of
   omega-6s to omega-3s.

   Retrieved from " http://en.wikipedia.org/wiki/Omega-3_fatty_acid"
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